The invention relates to a method of controlling inter-vehicle gap(s) in a platoon comprising a lead vehicle and one or more following vehicles. The invention also relates to a computer program, a computer readable medium, and a control unit for controlling inter-vehicle gap(s) in a platoon. The invention can for example be applied in heavy-duty vehicles, such as trucks and buses.
Automotive industry, research industry and others have explored possibilities to drive road vehicles in so called “platoons” or “road trains” with small time gaps mainly in order to save fuel but also to decrease driver workload and road footprint. The small time gap is enabled by vehicle-to-vehicle (V2V) communication and automation of longitudinal control. The level of both longitudinal and lateral control can differ between different platooning concepts and road environments.
Normally, the lead vehicle in the platoon strives to maintain a target speed and the vehicles behind in the platoon aims to copy the longitudinal control with the additional constraint to maintain the time gap to the vehicle in front in case it for some reason should not be able to adopt its speed to the lead vehicle. However, risks of too long response time of the V2V communication and too varying brake performance of the vehicles in the platoon may make the desired time gap sizes impossible.
WO2013/147684 discloses a method for spacing adjustment in a moving vehicle train formed of at least two vehicles, comprising the steps of continuously maintaining communication between the train's vehicles, continuously determining parameters which characterise the train's journey, and using parameters thus determined as a basis for determining suitable mutual spacing for the train's vehicles, wherein the step of determining said suitable mutual spacing of the train's vehicles comprises the step of using identified risk factors with a probability indication for each risk factor as a basis for evaluating the risk generated by said risk factors and adjusting said spacing accordingly. A local factor incorporation means which take account of local factors in relation to the vehicle train's journey comprise traffic situation determination means for determining prevailing and/or expected traffic situations in relation to the journey of the train's vehicles which might affect safety with regard to the spacing between the vehicles and might thus constitute a risk factor. The traffic situation determination means comprise sensor means situated on board vehicles in the train to monitor other vehicles in their vicinity and other objects such as other road users, e.g. cyclists or pedestrians or obstacles to, for example, the train's leading vehicle. However, a drawback with WO2013/147684 is that the incorporation of a probability indication, such as “slight”, for each risk factor can make the method imprecise and unpredictable. Imprecise and unpredictable risk factor assessments may yield a “just-to-be-safe” margin which often will degrade the gain of platooning and cooperative ACC (adaptive cruise control) by larger following gaps and more frequent dissolving.
It is desirable to provide an improved method of controlling inter-vehicle gap(s) in a platoon, which method may overcome or at least alleviate the above-mentioned and other drawbacks.
According to a first aspect of the invention, there is provided a method of controlling inter-vehicle gap(s) in a platoon comprising a lead vehicle and one or more following vehicles, wherein the method comprises the steps of: obtaining an indicator of a potential collision threat identified by an autonomous emergency braking system of the lead vehicle, wherein the autonomous emergency braking system of the lead vehicle comprises pre-defined control phases, and wherein the indicator at least partly determines a current control phase of the autonomous emergency braking system; and sending the obtained indicator to the one or more following vehicles. These steps may be performed by the lead vehicle.
The pre-defined control phases of the autonomous emergency braking system may for example be standardized or statutory. The present invention is based on the understanding that by sending said indicator obtained from the lead vehicle's autonomous emergency braking system to the following vehicle(s), the following vehicle(s) can due to the pre-defined control phases of the autonomous emergency braking system predict what the lead vehicle will do and take appropriate pre-emptive action. The method may further comprise: receiving, in the one or more following vehicles, said indicator; and automatically adjusting the inter-vehicle gap(s) based on the received indicator.
The indicator may be time to collision (TTC). Other indicators could be relative speed between the potential collision threat and the lead vehicle, distance between the potential collision threat and the lead vehicle, etc.
Automatically adjusting the inter-vehicle gap(s) based on the received indicator may include: a following vehicle of the one or more following vehicles subtracting a predetermined time from said time to collision depending on the following vehicle's position in the platoon, resulting in a reduced time to collision; and said following vehicle adjusting its gap to the preceding vehicle based on the reduced time to collision. The last vehicle of the platoon may for example subtract the longest time, the penultimate vehicle may subtract the second-longest time, and so on. In this way, the platoon may smoothly stretch out a safety margin distance between the individual vehicles beginning from its end. Automatically adjusting the inter-vehicle gap(s) based on the received indicator may start with the last vehicle of the platoon increasing its gap to the preceding vehicle.
Automatically adjusting the inter-vehicle gap(s) based on the received indicator may be initiated prior to a full brake phase of the autonomous emergency braking system of the lead vehicle. This makes the method less sensitive to delays in communication between the vehicles of the platoon. Furthermore, a buffer distance may also have been built up to mitigate the effects of different braking capacity of the vehicles in the platoon.
The method may further comprise: presenting information relating to how the last vehicle of the platoon adjusts its gap to the preceding vehicle to a driver of the lead vehicle. This may allow the driver of the lead vehicle to adopt lateral and longitudinal control for avoiding increased gaps in the rear of the platoon. The information may for example be present via a human machine interface, such as a display.
Sending the indicator may be performed using vehicle-to-vehicle communication means. Receiving the indicator may also be performed using vehicle-to-vehicle communication means. The indicator may for example be broadcast from the lead vehicle to the one or more following vehicles. Vehicle-to-vehicle communication may provide for fast communications between the vehicles of the platoon. However, communication via some infrastructure may also be possible.
The method may further comprise: determining a deceleration capacity for the lead vehicle based on a friction estimation. Furthermore, the step of automatically adjusting the inter-vehicle gap(s) based on the received indicator may include taking into account also said deceleration capacity. In this way, the lead vehicle may remain predictable for the following vehicles, even if a slippery road (low friction) reduces the deceleration capacity and calls for earlier braking.
According to a second aspect of the invention, there is provided a method of controlling inter-vehicle gap(s) in a platoon comprising a lead vehicle and one or more following vehicles, wherein the method is characterized by the steps of:
receiving, in the one or more following vehicles, an indicator of a potential collision threat identified by an autonomous emergency braking system of the lead vehicle, wherein the autonomous emergency braking system of the lead vehicle comprises pre-defined control phases, and wherein the indicator at least partly determines a current control phase of the autonomous emergency braking system; and automatically adjusting the inter-vehicle gap(s) based on the received indicator. These steps may be performed by the one or more following vehicles. This aspect may exhibit the same or similar features and/or technical effects as the first aspect of the invention.
The invention also relates to a computer program comprising program code means for performing steps of the first or second aspect of the invention when said program is run on a computer.
The invention also relates to a computer readable medium carrying a computer program comprising program code means for performing steps of the first or second aspect of the invention when said program product is run on a computer.
The invention also relates to a control unit for controlling inter-vehicle gap(s) in a platoon, the control unit being configured to perform steps of the first or second aspect of the invention. The control unit may for example be included in the lead vehicle and/or the following vehicle.
The invention also relates to a vehicle configured to perform steps of the first or second aspect of the invention.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.